Bài giảng TCP/IP Protocol - Chapter 10: Internet Group Management Protocol
Example 1 (Continued) Solution The events occur in this sequence: a. Time 12: The timer for 228.42.0.0 in host A expires and a membership report is sent, which is received by the router and every host including host B which cancels its timer for 228.42.0.0. b. Time 30: The timer for 225.14.0.0 in host A expires and a membership report is sent, which is received by the router and every host including host C which cancels its timer for 225.14.0.0. c. Time 50: The timer for 238.71.0.0 in host B expires and a membership report is sent, which is received by the router and every host.
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Chapter 10Upon completion you will be able to:Internet Group Management Protocol Know the purpose of IGMP Know the types of IGMP messages Understand how a member joins a group and leaves a group Understand membership monitoring Understand how an IGMP message is encapsulated Understand the interactions of the modules of an IGMP packageObjectives 1TCP/IP Protocol SuiteFigure 10.1 Position of IGMP in the network layer2TCP/IP Protocol Suite10.1 GROUP MANAGEMENTIGMP is a protocol that manages group membership. The IGMP protocol gives the multicast routers information about the membership status of hosts (routers) connected to the network. .3TCP/IP Protocol SuiteIGMP is a group management protocol. It helps a multicast router create and update a list of loyal members related to each router interface.Note:4TCP/IP Protocol Suite10.2 IGMP MESSAGES IGMP has three types of messages: the query, the membership report, and the leave report. There are two types of query messages, general and special. The topics discussed in this section include:Message Format5TCP/IP Protocol SuiteFigure 10.2 IGMP message types6TCP/IP Protocol SuiteFigure 10.3 IGMP message format7TCP/IP Protocol SuiteTable 10.1 IGMP type field8TCP/IP Protocol Suite10.3 IGMP OPERATIONA multicast router connected to a network has a list of multicast addresses of the groups with at least one loyal member in that network. For each group, there is one router that has the duty of distributing the multicast packets destined for that group. The topics discussed in this section include:Joining a GroupLeaving a GroupMonitoring Membership9TCP/IP Protocol SuiteFigure 10.4 IGMP operation10TCP/IP Protocol SuiteFigure 10.5 Membership report11TCP/IP Protocol SuiteIn IGMP, a membership report is sent twice, one after the other.Note:12TCP/IP Protocol SuiteFigure 10.6 Leave report13TCP/IP Protocol SuiteThe general query message does not define a particular group.Note:14TCP/IP Protocol SuiteFigure 10.7 General query message15TCP/IP Protocol SuiteImagine there are three hosts in a network as shown in Figure 10.8.Example 1See Next SlideA query message was received at time 0; the random delay time (in tenths of seconds) for each group is shown next to the group address. Show the sequence of report messages.16TCP/IP Protocol SuiteFigure 10.8 Example 117TCP/IP Protocol SuiteSolution The events occur in this sequence:Example 1 (Continued)a. Time 12: The timer for 228.42.0.0 in host A expires and a membership report is sent, which is received by the router and every host including host B which cancels its timer for 228.42.0.0.b. Time 30: The timer for 225.14.0.0 in host A expires and a membership report is sent, which is received by the router and every host including host C which cancels its timer for 225.14.0.0.c. Time 50: The timer for 238.71.0.0 in host B expires and a membership report is sent, which is received by the router and every host.See Next Slide18TCP/IP Protocol SuiteExample 1 (Continued)d. Time 70: The timer for 230.43.0.0 in host C expires and a membership report is sent, which is received by the router and every host including host A which cancels its timerfor 230.43.0.0.Note that if each host had sent a report for every group in its list, there would have been seven reports; with this strategy only four reports are sent.19TCP/IP Protocol Suite10.4 ENCAPSULATIONThe IGMP message is encapsulated in an IP datagram, which is itself encapsulated in a frame. The topics discussed in this section include:IP LayerData Link LayerNetstat Utility20TCP/IP Protocol SuiteFigure 10.9 Encapsulation of IGMP packet21TCP/IP Protocol SuiteThe IP packet that carries an IGMP packet has a value of 2 in its protocol field.Note:22TCP/IP Protocol SuiteThe IP packet that carries an IGMP packet has a value of 1 in its TTL field.Note:23TCP/IP Protocol SuiteTable 10.2 Destination IP addresses24TCP/IP Protocol SuiteFigure 10.10 Mapping class D to Ethernet physical address25TCP/IP Protocol SuiteAn Ethernet multicast physical address is in the range 01:00:5E:00:00:00 to 01:00:5E:7F:FF:FF.Note:26TCP/IP Protocol SuiteChange the multicast IP address 230.43.14.7 to an Ethernet multicast physicalExample 2Solution We can do this in two steps:a. We write the rightmost 23 bits of the IP address in hexadecimal. This can be done by changing the rightmost 3 bytes to hexadecimal and then subtracting 8 from the leftmost digit if it is greater than or equal to 8. In our example, the result is 2B:0E:07.b. We add the result of part a to the starting Ethernet multicast address, which is (01:00:5E:00:00:00). The result is01:00:5E:2B:0E:0727TCP/IP Protocol SuiteChange the multicast IP address 238.212.24.9 to an Ethernet multicast address.Example 3Solutiona. The right-most three bytes in hexadecimal are D4:18:09. We need to subtract 8 from the leftmost digit, resulting in 54:18:09..b. We add the result of part a to the Ethernet multicast starting address. The result is01:00:5E:54:18:0928TCP/IP Protocol SuiteFigure 10.11 Tunneling29TCP/IP Protocol SuiteWe use netstat with three options, -n, -r, and -a. The -n option gives the numeric versions of IP addresses, the -r option gives the routing table, and the -a option gives all addresses (unicast and multicast). Note that we show only the fields relative to our discussion.Example 4$ netstat -nra Kernel IP routing table Destination Gateway Mask Flags Iface 153.18.16.0 0.0.0.0 255.255.240.0 U eth0 169.254.0.0 0.0.0.0 255.255.0.0 U eth0 127.0.0.0 0.0.0.0 255.0.0.0 U lo 224.0.0.0 0.0.0.0 224.0.0.0 U eth0 0.0.0.0 153.18.31.254 0.0.0.0 UG eth0Any packet with a multicast address from 224.0.0.0 to 239.255.255.255 is masked and delivered to the Ethernet interface.30TCP/IP Protocol Suite10.5 IGMP PACKAGEWe can show how IGMP can handle the sending and receiving of IGMP packets through our simplified version of an IGMP package. In our design an IGMP package involves a group table, a set of timers, and four software modules.The topics discussed in this section include:Group TableTimersGroup-Joining ModuleGroup-Leaving ModuleInput ModuleOutput Module31TCP/IP Protocol SuiteFigure 10.12 IGMP package32TCP/IP Protocol SuiteFigure 10.13 Group table33TCP/IP Protocol Suite
